1. Field of the Invention
The present invention relates a continuous flow analytical apparatus for performing precipitation of a target component or impurities, separation of precipitates and analysis of a sample solution in flow injection analysis (referred to as "FI analysis" or "continuous flow analysis" hereinafter) for continuously analyzing the sample solution while flowing it through the capillary. The present invention also relates to a method of determining the amount of thiourea, while precipitating and separating impurities, in a copper electrolyte, on the basis of flow injection analysis (referred to as "FI analysis" or "continuous flow analysis" hereinafter) for continuously analyzing a sample solution while flowing it through a capillary.
2. Discussion of the Background
FI analysis is known in which a sample solution flowing through a capillary is introduced into an analytical portion after a reagent is added to the sample solution, to analyze a target component. An example is a method of measuring impurity concentrations in an electrolyte on the basis of FI analysis in which a buffer is added to a zinc electrolyte as a sample solution flowing through a capillary, reagents which are colored by Co ions and Cu ions in the solution are added to the solution, the sample solution is then introduced into a spectroscopic analyzer for measuring the absorbance of the solution, and the Co ion concentration and Cu ion concentration are determined from the absorbance (Japanese Patent Laid-Open No. 4-32764).
FI analysis has the advantages that a relatively small amount of sample can be precisely analyzed, and that addition of reagents and analysis can be carried out continuously, while flowing a sample solution through a capillary. Therefore, FI analysis is used in various fields. On the other hand, FI analysis requires preparation of a sample solution which produces no precipitate and uses reagents which produce no precipitate, as precipitates cause blocking of the capillary, in order to analyze the sample solution while flowing it through a capillary. Therefore, FI analysis is unsuitable for analysis of a sample solution which easily produces precipitates. Furthermore, when analysis must be performed after a target component or impurities are precipitated and separated, preliminary precipitation out of the system is required. In such a case, the advantages of continuous measurement are lost.
A copper electrolyte generally contains thiourea and glue or gelation added for stabilizing the properties of an electrodeposited metal. The state of electrodeposition is significantly affected by the concentration of these additive. Therefore, determination of these additives is important for controlling operation.
Several conventional methods are known for determining thiourea. An example is a method comprising measuring absorbance by using an iodine-starch solution as a color reagent, and determining the amount of thiourea on the basis of the amount of iodine consumed by the thiourea (Bulletin of the Mining Society of Japan/88 1007 ('72-1) pp.40-44). This method has the advantage of high measurement precision, but is labor intensive due to complicated control of the pH, reaction temperature and time. Since the concentration of an additive, such as thiourea, added to a copper electrolyte changes with time according to the pH, solution temperature and reaction time in the pretreatment process, quantitative analysis must be rapidly and precisely carried out under constant conditions. For example, thiourea in a solution immediately decomposes in the presence of copper and sulfuric acid to produce formidine disulfate, making it impossible to precisely and quantitatively measure the concentration.
A quantitative method is known in which this problem is solved by using FI analysis. In this method, a buffer, an iodine solution and a starch solution are added to a sample solution containing a copper electrolyte while flowing the sample solution through a capillary. The solution colored by the iodine-starch reaction is sent to an absorbance meter to determine the amount of thiourea (Japanese Patent Laid-Open No. 7-258879). This method has the advantage that addition of the reagents, coloring reaction and measurement of absorbance are performed continuously during the flow of the sample solution through the capillary, and thus the amount of thiourea can be determined within a short period of time. However, this method has the problem that the metal ions in the copper electrolyte must be removed in advance. Since the copper electrolyte contains trace amounts of reducing metal ions, such as iron, antimony, arsenic, bismuth, selenium, tin, tellurium, lead, etc., these ions react with the iodine, and therefore these metal ions must removed ahead of time in order to carry out the measurement by FI analysis. However, since FI analysis is performed by analyzing a sample solution while flowing it through a capillary, if precipitates are carelessly produced in removal of these metal ions, measurement might be impossible due to blocking of the capillary.
In the above conventional measurement method, ferric or/and lanthanum ions are initially added to the sample solution out of the system, to produce precipitates of metal impurities, and the precipitates are filtered off before the sample solution is used. As a result, the advantage of FI analysis, that continuous analysis can be made within a short period of time, significantly deteriorates.
The present invention solves the above problems of conventional FI analysis.